Underwater hydraulic system for reducing pump noise

Abstract

A hydraulic system which includes a pump for supplying hydraulic fluid to a load and receiving hydraulic fluid therefrom wherein the pump is acoustically isolated from the surrounding water medium. The pump and a motor which drives the pump is enclosed in a pressure vessel, the interior of which is supplied with a gas at a certain pressure less than the ambient water pressure. The pressure of the hydraulic fluid in the return line is maintained at a pressure less than the ambient by a reservoir arrangement which includes a piston and rod assembly with the rod being subject to the ambient water medium. A certain pressure within an oil filled compartment of the reservoir is maintained at a fraction of the ambient water medium pressure by making the ratio of the cross sectional area of the piston to the rod equal to that predetermined fraction. This reduced pressure compartment is hydraulically connected to the fluid return line as well as to a gas regulator.

I claim: 
     
       1. A hydraulic system for use in an underwater structure wherein hydraulic fluid is supplied to a load, comprising: A) a pressure vessel carried by said structure and exposed to the surrounding ambient water medium and including a pressurized gas therein;   B) a gas supply for pressurizing said pressure vessel;   C) a pump and drive motor therefor contained within said pressure vessel;   D) a hydraulic fluid supply line connecting said pump to said load;   E) a hydraulic fluid return line connecting said load back to said pump; and   F) means connected to said hydraulic fluid return line for maintaining the fluid pressure therein at a predetermined fraction of the pressure of the ambient water medium, where said predetermined fraction is less than 1.   
     
     
       2. Apparatus according to claim 1 wherein said means includes: A) a piston and rod assembly;   B) a housing containing said assembly in a manner that said piston divides said housing into first and second compartments and said rod is exposed to the ambient water pressure;   C) said first compartment containing a hydraulic fluid and said second compartment containing a gas at a relatively low pressure;   D) a first fluid line connecting said first compartment with said hydraulic fluid return line;   E) the axial cross sectional area "a" of said rod being smaller than the axial cross sectional area of "A" of said piston.   
     
     
       3. Apparatus according to claim 2 wherein: A) the ratio of a/A is equal to said predetermined fraction.   
     
     
       4. Apparatus according to claim 2 wherein: A) said piston is cylindrical.   
     
     
       5. Apparatus according to claim 2 wherein: A) said rod is cylindrical.   
     
     
       6. Apparatus according to claim 1 wherein said gas supply includes: A) a gas container;   B) a regulator for supplying the gas within said container to said pressure vessel at a certain pressure; and   C) means for communicating the hydraulic fluid return line pressure to said regulator for delivering gas to said pressure vessel at said return line pressure.   
     
     
       7. Apparatus according to claim 6 wherein the means for communicating the return line pressure includes: A) a second fluid line connected to said first fluid line.